"About two or three years ago when we first went into Birmingham an agent called us and said we are trying to get some of our younger players out to expose them to different levels," said Rowett, who now manages Derby County.
"We had a look at him (Lindelof) and put it to some of the staff, but it was ironic because they felt he wasn't probably quite tough enough.
"Then suddenly he's been touted around at £20m or £30m. So I think we made a mistake.
"To be fair he got straight back in the Benfica side very quickly and of course went from strength to strength."